Currently the display devices have the trend toward the thin and slim-bezel designs. These display devices include LCD TVs, LCD monitors, notebook PCs, consumer electronics, etc.
These thin and slim-bezel designs are accomplished by using the cascade circuit to transmit the transistor-transistor logic (TTL) signals instead of the originally frequently used reduced swing differential signaling (RSDS) signal. The usage of the cascade circuit to directly transmit the system signals in the substrate of the display device can reduce the quantity of the flexible printed circuit (FPC) to be used and the size of the printed circuit board (PCB). Besides the cost saving, the space in the bezel can be saved, and the thickness of the module can be reduced.
Please refer to FIG. 1, which is the schematic diagram showing the side view of the cascade circuit of the driver integrated circuit of the prior art. The connecting pads 11 and 12 are disposed on substrate 10. The insulating layer 14 covers substrate 10 and connecting pads 11 and 12. The portions of the insulating layer 14 just above connecting pads 11 and 12 are etched to form small openings. The metal line 18 is coated on the portion of insulating layer 14 between connecting pads 11 and 12. Then, protecting layer 15 is coated above metal line 18 and insulating layer 14. The portion of protecting layer 15 right above connecting pads 11 and 12, and the top portions of metal line 18 close to two ends are etched to form openings. The transparent connecting layers 16 and 17 are coated above these openings to be electrically connected with the conducting elements (not shown in FIG. 1), e.g. the bump of driver IC chip, of the integrated circuit. It can be seen from FIG. 1 that connecting pad 11 is electrically connected with connecting pad 12 through transparent connecting layer 17, metal line 18 and transparent connecting layer 16 so as to reach the function of transmitting signals.
Although the cascade techniques have successfully made the products into a slim shape, some problems ensue in the following.
(I) Two band issue: For an example of a product with 800×480 pixels, since the cascade circuit replaces the past configuration of one FPC corresponding to one IC, the IC is used to drive the next IC instead. Therefore, the power line must pass the conducting line on the glass for the transmissions. Since the impedance of the metal material on the glass is larger than that of the copper wire of FPC, the impedance of the conducting line and the induced capacity become too large, i.e. RC loading too large, and accordingly the electrical power decays to cause unusual signals outputted by the IC and to result in the phenomenon of two bands. For example, the upper and lower blocks with different brightness appear on the screen.
(II) Electromagnetic interference (EMI) issue: The issue of impedance matching needs to be considered under the high-frequency operation. When the impedance is not matched or not well matched, the signals from the transmitting end can not be completely received by the receiving end, and will be reflected to result in electro-magnetic scattering and to cause the EMI effect. The current solutions are done by increasing the distance between the conducting lines (for example, the distance between the metal lines 18 in FIG. 1) and by improving the shapes of the conducting lines. Then more space is needed, the impedance of the conducting line can not be reduced, and the driving power of IC will be affected to result in the problem of two bands.
In order to solve the above mentioned problems and to meet the market requirements, the development team of the present invention has done a lot of deep analyses and researches. Finally the novel circuit structures are developed after plenty of experiments and improvements with the proofs of being able to solve the above mentioned two problems after a lot of trials, and can meet the requirements of the thin and slim-bezel designs. The present invention is described below.